1. Field of the Invention
Generally, the present invention relates to surgical devices. More specifically, the present invention relates to surgical devices for fastening tissues, closing tissues, and repairing tissues such as a mitral valve.
2. Description of Related Art
Minimally invasive surgery has allowed physicians to carry out many surgical procedures with less pain and disability than conventional, open surgery. In performing minimally invasive surgery, the surgeon makes a number of small incisions through the body wall to obtain access to the tissues requiring treatment. Typically, a trocar, which is a pointed, piercing device, is delivered into the body with a cannula. After the trocar pierces the abdominal or thoracic wall, it is removed and the cannula is left with one end in the body cavity, where the operation is to take place, and the other end opening to the outside. A cannula has a small inside diameter, generally 3-10 millimeters. A number of such cannulas are inserted for any given operation.
A viewing instrument, typically including a miniaturized video camera, is inserted through one of these cannulas and a variety of surgical instruments and retractors are inserted through others. The image provided by the viewing device may be displayed on a video screen or television monitor, affording the surgeon enhanced visual control over the instruments. Because a commonly used viewing instrument is called an “endoscope,” this type of surgery is often referred to as “endoscopic surgery.” In the abdomen, endoscopic procedures are commonly referred to as laparoscopic surgery, and in the chest, as thoracoscopic surgery. Abdominal procedures may take place either inside the abdominal cavity (in the intraperitoneal space) or in a space created behind the abdominal cavity (in the retroperitoneal space). The retroperitoneal space is particularly useful for operations on the aorta and spine.
Minimally invasive surgery has virtually replaced open surgical techniques for operations such as cholecystectomy and anti-reflux surgery of the esophagus and stomach. This has not occurred in either peripheral vascular surgery or cardiovascular surgery. An important type of vascular surgery is to replace or bypass a diseased, occluded, or injured artery. Arterial replacement or bypass grafting has been performed for many years using open surgical techniques and a variety of prosthetic grafts. These grafts are manufactured as fabrics (often from Dacron or Teflon) or are prepared as autografts (from the patient's own tissues) or heterografts (from the tissues of animals). A graft can be joined to the involved artery in a number of different positions, including end-to-end, end-to-side, and side-to-side. This attachment between artery and graft is known as an anastomosis. Constructing an arterial anastomosis is technically challenging for a surgeon in open surgical procedures, and is almost a technical impossibility using minimally invasive techniques.
Minimally invasive surgery is of interest in cardiovascular surgery because of the nature of the tissue of the heart. Cells known as myocytes beat together in unison in a healthy heart when ion channels open and close in an organized manner. Ions pass in and out of the channels, and the change in concentration of ions from within a cell to outside of a cell results in an electrical potential, causing the cell itself to depolarize and repolarize. The depolarization of one cell triggers the cell next to it to depolarize, and thus a cascade effect of depolarization of all the myocytes is triggered and the heart beats. Making several incisions can interrupt this cascade during surgery and change the beating of the heart. Keeping incisions to a minimum with minimally invasive techniques will allow beating heart surgery to be successful while maintaining the electrical integrity of the heart.
Many factors contribute to the difficulty of performing arterial replacement or bypass grafting. See generally, Wylie, Edwin J. et al., Manual of Vascular Surgery, (Springer-Verlag New York), 1980. One such factor is that the tissues to be joined must be precisely aligned with respect to each other to ensure the integrity and patency of the anastomosis. If one of the tissues is affixed too close to its edge, the suture can rip through the tissue and impair both the tissue and the anastomosis. Another factor is that, even after the tissues are properly aligned, it is difficult and time consuming to pass the needle through the tissues, form the knot in the suture material, and ensure that the suture material does not become tangled. These difficulties are exacerbated by the small size of the artery and graft. The arteries subject to peripheral vascular and cardiovascular surgery typically range in diameter from several millimeters to several centimeters. A graft is typically about the same size as the artery to which it is being attached. Another factor contributing to the difficulty of such procedures is the limited time available to complete the procedure. The time the surgeon has to complete an arterial replacement or bypass graft is limited because there is no blood flowing through the artery while the procedure is being done. If blood flow is not promptly restored, sometimes in as little as 30 minutes, the tissue the artery supplies may experience significant damage, or even death (tissue necrosis). In addition, arterial replacement or bypass grafting is made more difficult by the need to accurately place and space many sutures to achieve a permanent hemostatic seal. Precise placement and spacing of sutures are also required to achieve an anastomosis with long-term patency.
Highly trained and experienced surgeons are able to perform arterial replacement and bypass grafting in open surgery using conventional sutures and suturing techniques. A suture has a suture needle that is attached to a long, trailing suture material. The needle must be precisely controlled and accurately placed through both graft and artery. The trailing suture material must be held with proper tension to keep the graft and artery together, and must be carefully manipulated to prevent the suture material from tangling. In open surgery, these maneuvers can usually be accomplished within the necessary time frame, thus avoiding the subsequent tissue damage (or tissue death) that can result from prolonged occlusion of arterial blood flow.
The difficulty of suturing a graft to an artery using minimally invasive surgical techniques has effectively prevented the safe use of this technology in both peripheral vascular and cardiovascular surgical procedures. In some minimally invasive procedures, such as those in the abdominal cavity, the retroperitoneal space, or chest, the space in which the operation is performed is more limited. The exposure to the involved organs is also more restricted than with open surgery. Moreover, in a minimally invasive procedure, the instruments used to assist with the operation are passed into the surgical field through cannulas. When manipulating instruments through cannulas, it is extremely difficult to position tissues in their proper alignment with respect to each other, pass a needle through the tissues, form a knot in the suture material once the tissues are aligned, and prevent the suture material from becoming tangled. Therefore, although there have been isolated reports of vascular anastomoses being formed by minimally invasive surgery, no system has been provided for widespread surgical use that would allow such procedures to be performed safely within the prescribed time limits.
Anastomoses are commonly formed in open surgery by suturing together the tissues to be joined. However, one known system for applying a clip around tissues to be joined in an anastomosis is disclosed in a brochure entitled, “VCS Clip Applier System”, published in 1995 by Auto Suture Company, a Division of U.S. Surgical Corporation, wherein a clip is applied by a clip applier about the tissues in a nonpenetrating manner, such that the clip does not penetrate through the tissues, but rather is clamped down around the tissues. It is imperative in forming an anastomosis that tissues to be joined are properly aligned with respect to each other. The clip applier has no means for positioning tissues to ensure proper alignment. Before the clip can be applied, the tissues must first be grasped and properly positioned with respect to each other, for example, by skewering the tissues with a needle as in common suturing techniques, and/or with forceps to bring the tissues together. It is extremely difficult to perform such positioning techniques in minimally invasive procedures within the confines of the cannulas.
Coalescent Surgical, Inc. also produces a U-CLIP Anastomotic Device based on self-closing clip technology of nitinol, which eliminates knot tying. The disadvantage of this system is that the surgeon needs to guide the needle from the graft through the native tissue before the U-CLIP can be deployed to suture the tissue.
Further, when performing mitral valve repairs, it is important to understand that the mitral valve depends on adequate apposition or alignment between the anterior and posterior leaflets along a relatively long surface area under high pressure conditions. Typically, the contact surface is about 12 mm in a direction perpendicular to the anterior-posterior direction and this provides little margin of safety. The leaflet margins are attached to numerous fine chords suspended from attachment points along the inner surface of the left ventricle. Although these attachments are often referred to as papillary muscles, there is often a very diffuse arc-shaped attachment for each of the groups of chords to the endocardial surface. Unfortunately, this anchor point (i.e., the inner wall of the left ventricle) must move with each heartbeat and so the distance between the attachment of the leaflet edges is constantly changing. The chordal lengths may also change, typically increasing with age and degeneration, and the chords frequently do not lengthen in a symmetrical fashion. This leads to variations in the chordal lengths at all-important points of coaptation. Chords may also rupture. In addition, the mitral annulus changes diameter with each heartbeat such that its surface area changes by about 40% with each systole. As the heart enlarges, the annulus of the mitral valve can enlarge as well. In short, there are many variables affecting proper functioning of the mitral valve. The anatomy, such as the leaflet length, the chordal length, and the annular length/diameter, can change. The attachment points can change as the ventricle changes shape. More importantly, all of these aspects can change simultaneously. For example, a patient may have ischemic mitral regurgitation that pulls the posteriolateral valve attachments away from their natural coaptation points and leads to an opening in this area of the mitral valve. This can be further affected if the chordal lengths are changed by even minor degrees of degenerative disease.
Current surgical practice for mitral valve repair generally requires that the mitral valve annulus be reduced in radius by surgically opening the left atrium and then fixing sutures, or more commonly, sutures in combination with a support ring, to the internal surface of the annulus; this structure is used to cinch the annulus, in a purse-string-like fashion, to a smaller radius, thereby reducing mitral regurgitation by improving leaflet coaptation.
This method of mitral valve repair, generally termed “annuloplasty”, effectively reduces mitral regurgitation in heart failure patients. This, in turn, reduces symptoms of heart failure, improves quality of life, and increases longevity. Unfortunately, however, the invasive nature of mitral valve surgery and the attendant risks render most heart failure patients poor surgical candidates. Thus, a less invasive means to increase leaflet coaptation and thereby reduce mitral regurgitation in heart failure patients would make this therapy available to a much greater percentage of patients.
Mitral regurgitation also occurs in approximately 20% of patients suffering acute myocardial infarction. In addition, mitral regurgitation is the primary cause of cardiogenic shock in approximately 10% of patients who develop severe hemodynamic instability in the setting of acute myocardial infarction. Patients with mitral regurgitation and cardiogenic shock suffer approximately a 50% hospital mortality. Elimination of mitral regurgitation in these patients would be of significant benefit. Unfortunately, however, patients with acute mitral regurgitation complicating acute myocardial infarction are particularly high-risk surgical candidates, and therefore, are not good candidates for traditional annuloplasty. Thus, a minimally invasive means to effect a temporary reduction or elimination of mitral regurgitation in these critically ill patients would afford them the time to recover from the myocardial infarction or other acute life-threatening events, and make them better candidates for medical interventional or surgical therapy.
It would, therefore, be useful to develop a surgical clip for use in minimally invasive surgeries.